1. Field of the Invention
This invention relates to aminocarboxylic acid salts. More particularly, this invention relates to a method for the manufacture of aminocarboxylic acid salts by the reaction of amino alcohols in the presence of an alkali metal compound.
2. Description of Prior Art
Aminocarboxylic acid salts find utility in various applications. The glycine salt, for example, is generally neutralized into glycine and, as such, is widely used as an additive in processed meat, refreshing beverage, instant food and other processed foodstuffs. It is also used widely as raw material for pharmaceuticals, agricultural chemicals and pesticides and amino acids. The iminodiacetic acid salt is generally neutralized into iminodiacetic acid and is used in various applications utilizing the action of chelation and is also used as raw material for agricultural chemicals and pharmaceuticals. The nitrilotriacetic acid salt, because of its outstanding chelating ability, is extensively used in watersoftening agent, scouring aid, dyeing assistant, paper-coating agent, scale inhibitor, detergent builder and agent for preventing soap from degeneration.
For commercial production of such aminocarboxylic acid salts, the Strecker Process which uses hydrogen cyanide and formaldehyde as principal raw materials is generally known. Since hydrogen cyanide is violently toxic, the equipment for production, the handling of raw materials and the selection of site for plant, etc. are strictly restricted. Since the majority of the hydrogen cyanide is obtained as a by-product in the manufacture of acrylonitrile, the hydrogen cyanide causes a serious problem about the steady acquisition of raw material.
It has been known to the art to produce aminocarboxylic acid salt by oxidative dehydrogenation of amino alcohol in the presence of an alkali hydroxide (U.S. Pat. Nos. 2,384,816. 2,384,817. 3,535,373. 3,842,081 and 3,739,012). For example, U.S. Pat. No. 2,384,816 discloses a method for effecting the production of glycine salt by the reaction of monoethanolamine with alkali metal hydroxides in the absence of catalyst. This method has a disadvantage that the reaction consumes much time and glycine salt is obtained in low yields. U.S. Pat. No. 2,384,817 discloses a method involving the reaction of monoethanolamine with potassium hydroxide at elevated temperatures in the form of flakes in the presence of a copper catalyst in the absence of water. But it does not disclose the yield of glycine salt. The same patent discloses a method for the reaction of monoethanolamine with potassium hydroxide in the presence of cadmium oxide which is poisonous under the same conditions, but the yield of glycine salt is low. Further, U.S. Pat. No. 3,842,081 discloses a method for producing an iminodiacetic acid salt by the reaction of diethanolamine with sodium hydroxide in the presence of a cadmium oxide catalyst. This method gives the product at realtively high yields. U.S. Pat. Nos. 3,535,373. 3,578,709 and 3,739,021 disclose a method for producing nitrilotriacetic acid salt by the reaction of triethanolamine with alkali metal hydroxides in the presence of a cadmium oxide catalyst. This method gives the product in rather high yields. Then, U.S. Pat. No. 3,578,079 discloses a method for the reaction of triethanolamine with alkali metal hydroxides in the presence of a zinc oxide catalyst. This method does not give the product in satisfactory yields.
The conventional methods are such that the reactions using no catalyst and the reactions using zinc oxide as a catalyst give their products in very low yields. Further, the methods which use a cadmium oxide catalyst have a possibility that the cadmium compound which is toxic will contaminate the reaction product and, by reason of this possibility, cannot be adopted where the use found for the reaction product does not tolerate the presence of the cadmium compound. Moreover, the plant effluent entraining the cadmium compound flows into a nearby river and lake, it will raise a serious social problem. On the other hand, U.S. Pat. No. 2,284,817 does not disclose the reaction in the presence of water, when copper is used as the catalyst. U.S. Pat. No. 2,384,818 shows that the reation of monoethanolamine in the absence of water gives low yield.
An object of this invention, therfore, is to provide a novel method for the manufacture of an aminocarboxylic acid salt.
Another object of this invention is to provide a method for the manufacture of an aminocarboxylic acid salt by the dehydrogenation of an amino alcohol in the presence of an alkali metal compound without involving use of a cadmium compound which is dangerous because of toxicity.